Thameslink Programme has untangled the track on the approaches to London Bridge station to reduce the time trains wait for platforms to clear and cut delays. To achieve this, new track and infrastructure has been added – including a major new structure called the Bermondsey Dive Under.
This new junction enables each train service to have its own dedicated line into and out of London Bridge station. Southeastern trains travelling from Kent ‘dive under’ the Sussex lines used by Southern and Thameslink trains. This relieves the bottleneck which had developed over time in this area, known as Bricklayers Arms Junction.
Previously this historic section of track, which dated back over 150 years, featured some of the most complex track layouts anywhere in the world, contributing to delays in and out of the station. The new infrastructure added will make journeys more reliable for millions of passengers travelling to and through London Bridge.
Built in the shadow of Millwall’s New Den stadium, construction work on the Dive Under began in the spring of 2012 and was completed in December 2016. The first passenger train service ran through the new junction on 3 January 2017. The Dive Under is formed of 11 new interconnected structures, along the line of existing operational rail viaducts.
Before it was built, the lines to Sussex and Kent criss-crossed over each other at a series of flat junctions, causing delays and limiting the number of trains that could travel per hour. The new structure reduces delays outside London Bridge by creating a ‘grade separated’ junction, allowing unimpeded access for trains moving through this junction and onwards to London Bridge station. Improving the flow of trains through this area not only reduces delays caused by having to wait in this area, but also means we can introduce more trains into the timetable.
As part of the work, 20 bridges between New Cross and Waterloo East were also strengthened.
Despite being adjacent to one another, these lines are now essentially separate railways that do not interact with one another after they pass through the Bermondsey Dive Under on the approach to London Bridge. This instils resilience in to the network that was not there previously – when there is a problem on one set of lines, the knock impact on other lines is reduced. This is important in such a congested stretch of railway.
Dedicated lines and platforms also means the space available for Thameslink services through London Bridge has been hugely increased in peak hours – from one train per hour before work started compared to up to sixteen per hour by the end of the programme.
Wherever possible, existing structures were reused, to minimise disruption and reduce waste. Although some old viaducts had to be replaced by modern structures, they have been designed to remain in keeping with the older architecture, with the new arches having a similar form compared to the existing masonry arches.
This also ensured that the load distribution on the original foundations remained relatively unchanged, allowing for many of the existing piers to be reused. This contributed significantly to reducing the number of new foundation structures required, meaning the work could be completed quicker, at a lower cost and with less disruption from heavy construction work.
The Thameslink Programme is committed to increasing net positive biodiversity on its projects. Prior to construction, the site had a low conservation value and limited botanical diversity.
The soil was heavily contaminated with hydrocarbons and asbestos, as well as the invasive species Japanese Knotweed. The project saw the eradication of the Japanese Knotweed and the removal of over 21,900 tonnes of contaminated material. Furthermore, wildflower planting and the installation of 765 square metres of green walls has increased the site’s biodiversity and helped the team achieve a CEEQUAL score of 96.6%, having increased biodiversity in the area by 113%.
The team also carried out extensive community engagement, including upgrading the garden in the Lewisham Community Centre, refurbishing a youth club in a local church and volunteering on the XLP youth charity bus.
During the work to demolish a number of the existing viaducts, Thameslink Programme engineers discovered the ghostly remains of a long-lost South London railway station which closed more than 100 years ago.
Southwark Park station, perched on a viaduct above Rotherhithe New Road, only served passengers from 1902 to 1915 before it closed for good. The old ticket hall, booking hall and platforms were revealed, with the arch which held the booking hall retained.
The works at Bermondsey Dive Under (BDU) required the execution of a major civil engineering project near the operational railway.
Key lessons from what went well on the project including: integrated planning and relationship management, management of third party relationships, integrated working, change management, Value Engineering and scheme handback and close-out. The case study also looks at what could have been improved, including contract content, contract administration and rework/redesign costs, and proposes recommendations for future schemes.
How collaboration and incentivisation were crucial to successful delivery of Key Output 2, including the re-signalling, track remodelling and construction of London Bridge station, construction of the Bermondsey Dive Under to the east and Borough Viaduct to the west.